Production of thiocyanogen

ABSTRACT

Thiocyanogen is generated by introducing a halogen into an aqueous solution of a water-soluble thiocyanate salt having a water-insoluble liquid organic thiocyanogen-solvent admixed therewith, thereby extracting the thiocyanogen into the organic solvent phase as it is formed.

United States Patent Welcher 5] Mar. 14,1972

[541 PRODUCTION OF THIOCYANOGEN [72] Inventor: Richard Parke Welcher,Old Greenwich,

[21] Appl. No.: 729,338

[52] US. Cl ..23/357, 23/359 [51] Int. Cl ...C0lb 21/54, C01b 31/00 [58]Field of Search ..23/357, 359, 151

3,047,363 7/1962 Fieldetal. ..23/l5l CHL OFF/IVE AQUEOUS SOD/UMTH/OCYANA TE SOL U T/ON Primary Examiner0scar R. Vertiz AssistantExaminer-Hoke S. Miller Attomey-James H. Laughlin, Jr.

[ ABSIRACT Thiocyanogen is generated by introducing a halogen into anaqueous solution of a water-soluble thiocyanate salt having awater-insoluble liquid organic thiocyanogen-solvent admixed therewith,thereby extracting the thiocyanogen into the organic solvent phase as itis formed.

COOL M/G BR/NE 9 Claims, 1 Drawing Figure BE/VZENE TH/O CYANOGE/VSOLUTION 5 PATENTEU R 14 I972 3, 649 221 CHLOE/IVE Q 9 BE/VZENE L Q9A0u0us SOD/UM m/ocmma TE SOLUTION CYANOGE/V 12 SOLUTION coomva BR/NE ISALT WATER INVENTOR. RICHARD PARKE WELCHER A TTORNE Y PRODUCTION OFTHIOCYANOGEN This invention relates to a method for the production ofthiocyanogen, a compound of the formula (SCN that is used as ananalytical reagent and in the production of alkyl and alkylenebis-thiocyanate and aryl monothiocyanate insecticides and germicides.Principal objects of the invention are to provide a method whereinthiocyanogen can be produced at a relatively rapid rate and preferablycontinuously, and in which it is obtained as a solution in an organicsolvent such as benzene or toluene. A further object is to provide amethod whereby thiocyanogen can be obtained in high yields by thereaction of an aqueous solution of a water-soluble thiocyanate salt witha halogen while avoiding substantial hydrolysis or polymerization. Stillfurther objects of the invention will become apparent from the followingdetailed description, when taken with the appended claims.

Heretofore thiocyanogen has been regarded as a highly unstable material.its sensitivity toward hydrolysis and polymerization is such that it hasbeen liberated in a free condition from thiocyanate salts only innonaqueous systems, and in most preparations it is produced in situ asit is reacted. Thus in the preparation of a p-thiocyanoaniline asolution of sodium thiocyanate and aniline in methanol is reacted withbromine at low temperatures, thus forming the thiocyanoaniline directly.

My present invention is based on the discovery that thiocyanogen can beobtained in good yields, and with a minimum of hydrolysis andpolymerization, by generating it in an aqueous solution of awater-soluble thiocyanate salt provided a water-insoluble liquid organicsolvent for thiocyanogen is admixed therewith. l have found that whenthis is done the thiocyanogen is extracted from the water phase into theorganic solvent phase as fast as it is formed, thus protecting theproduct thiocyanogen from hydrolysis or polymerization. Sincethiocyanogen is liberated from aqueous thiocyanate salt solutions by theaction of halogens at a much faster rate than can be obtained at lowtemperatures in a nonaqueous organic solvent system, the process of myinvention is well adapted for commercial-scale production.

Although any watersoluble thiocyanate salt may be used as a startingmaterial in the process of the invention the inorganic salts such as thealkali metal, ammonium and alkaline earth metal thiocyanates arepreferred for a number of practical reasons. All of these inorganicthiocyanates are very water soluble, and can therefore be used asconcentrated aqueous solutions; the importance of this will subsequentlybe explained. Furthermore, all of these thiocyanates form watersolublehalides with chlorine, bromine, fluorine and iodine, and the resultingbrine solutions assist in the extraction of thiocyanogen into theorganic phase.

A wide variety of liquid organic thiocyanogen solvents may be used inthe process; in fact, any such solvent may be employed that is waterinsoluble. As a practical matter, however, hydrocarbon solvents aregreatly preferred since thiocyanogen is known to deteriorate in thepresence of many solvents of other types such as hydroxylic organicsolvents. The preferred organic solvents to be used in practicing theinvention are therefore the liquid mononuclear aromatic hydrocarbonssuch as benzene, toluene, ethyl benzene, ortho-xylene, meta-xylene andthe like.

It is an important advantage of the invention that it is well adapted tocontinuous manufacturing processes. Thus, a halogen such as chlorine canbe continuously introduced into an agitated reaction vessel containingwater having an alkali metal thiocyanate dissolved therein while anorganic solvent such as benzene and additional aqueous thiocyanatesolutions are preferably continuously introduced. The thiocyanogenliberated from the alkali metal thiocyanate solution by the oxidizingaction of the chlorine is immediately taken up by the benzene ortoluene, which forms a supernatant layer that can readily be drawn offand the thiocyanogen recovered if desired.

It is another important advantage that the solutions of thiocyanogen inliquid organic solvents such as benzene, toluene or xylene mixtures,produced by the process of the invention and therefore not necessarilyanhydrous, can be reacted effectively with alpha-olefms and acetylenesin the presence of a free radical initiator such as a free radicalcatalyst or actinic light. Examples of such reactions will be givenlater. However, processes wherein such thiocyanogen solutions arereacted in this manner are not claimed in the present application asthey are a portion of the claimed subject matter of my copendingapplication Ser. No. 729,375 filed concurrently herewith.

The invention will be further described with reference to theaccompanying drawing, the single FIGURE of which is a diagrammaticillustration of a reaction vessel in which a continuous process is beingcarried out. On this drawing reference numeral 1 indicates a reactionkettle which is preferably glass lined, since thiocyanogen is quitecorrosive. The kettle l is provided with a cooling jacket 2 and anagitator 3 and also with a side discharge line 4 having a valve 5 and abottom discharge line 6 provided with a valve 7. Benzene or otherorganic solvent is introduced through a valved inlet pipe 8, whichpreferably discharges into the propeller 3, and chlorine and sodiumthiocyanate solutions are introduced through lines 9 and 10respectively.

In operation a heel of aqueous sodium thiocyanate solution is chargedinto the reaction kettle, as is indicated generally by reference numeral11. Benzene or other water-immiscible solvent is admitted through line 8as chlorine is introduced through line 9, the agitator 3 being inoperation to insure admixture of the organic solvent with the water.Simultaneously, sufficient brine is passed through the jacket 2 tomaintain a temperature below 20 C. and preferably below 10 C., sinceimproved yields are obtained at reaction temperatures in the range ofabout 0 to 10 C. or lower. When a steady state has been established,additional sodium thiocyanate solution is introduced preferablycontinuously through the line 10.

Thiocyanogen is formed in the aqueous phase by the reaction ZNaSCN C1(SCN) 2NaCl but is extracted into the benzene or toluene phase as fastas it is produced. Because of this continuous and rapid extraction thereis very little loss due to polymerization and practically no hydrolysisof the thiocyanogen. The benzene or toluene solution collects as asupernatant organic phase 12 above the water phase 11 and is drawn offthrough the outlet line 4. Brine solution is preferably continuouslywithdrawn through the line 6 at a rate roughly equivalent to the rate atwhich sodium thiocyanate solution is introduced.

The thiocyanate solution produced in this manner may be dried byadmixture with any suitable drying agent and passed to storage, since itis known that solutions of thiocyanogen in benzene or toluene arestorage stable. If other solvents such as ethyl acetate or carbontetrachloride are used it is advisable to use the solution morepromptly, as thiocyanogen solutions in this type of solvent are lessstable.

ln practicing the process of my invention, best results are obtained bycontrolling the amounts of water and organic solvent used. For goodresults sufficient water should always be present to dissolve thethiocyanate salt completely, as otherwise phase difficulties areencountered. It is also important, however, to form a concentratedsolution of alkali metal, ammonium or alkaline earth metal halide, asthis assists the rapid and complete extraction of thiocyanogen into thewater-immiscible organic solvent. For this reason it is greatlypreferable to add the thiocyanate salt as a concentrated aqueoussolution, and in general a weight ratio of alkali metal thiocyanate towater should be used that is not greater than about 1.5 to 1 nor lessthan about 0.3 to l.

The ratio of water to toluene, benzene or.other water-immisciblethiocyanogen solvent should also preferably be controlled. Three partsby weight of the solvent for each part of water is the minimum preferredamount that will produce commercially acceptable yields, and with mostsolvents the preferred ratio will be within the range of about five to10 parts by weight of organic solvent for each part of water. When theseratios are maintained the process operates smoothly and the thiocyanogenis recovered in optimum yields.

The invention will be further described and illustrated by the followingspecific examples, wherein preferred embodiments are given. It will beunderstood, however, that although these examples may describe some ofthe more detailed aspects of the invention, they are given primarily asillustrations and the invention in its broader aspects is not limitedthereto.

EXAMPLE 1 The reaction kettle 1 was charged with 135 parts by weight ofa 60 percent solution of sodium thiocyanate in water which had beencooled to C. The agitator 3 was started and streams of benzene andchlorine were introduced at rates such that about eight to parts byweight of benzene were added for each part of thiocyanogen formed. Afterabout 30 parts by weight of chlorine had been introduced the valve inline 10 was opened and 60 percent aqueous thiocyanate solution wasadmitted at a rate corresponding to the addition of 2 mols of sodiumthiocyanate for each mol of gaseous chlorine (C1 The temperature withinthe kettle was maintained at about 5 10 C. by circulating cold brinethrough the cooling jacket.

Thiocyanogen was produced in the water phase by the reaction of chlorinewith the aqueous sodium thiocyanate solution but was immediatelyextracted into and protected by the benzene present. The resultingbenzene solution of thiocyanogen rose to the top of the aqueous phaseand was withdrawn through side outlet 4.

It will be understood that in this process the benzene can be replacedby corresponding amounts of other water-immiscible liquid thiocyanogensolvents such as toluene, ethylbenzene, ortho-xylene, meta-xylene andother mononuclear aromatic hydrocarbons. Some of these solvents, e.g.,toluene, do not separate immediately when dispersed in water at lowtemperatures and it may therefore be advisable to withdraw a twophasemixture of thicyanogen-containing solvent and water from the side outlet4 into a separating tank, where the water can be separated anddischarged to waste.

it will also be understood that any water-soluble thiocyanogen salt maybe used in the process of this example. Thus, corresponding quantitiesof ammonium thiocyanate, of any other alkali metal thiocyanate, or of analkaline earth metal cyanate such as calcium or barium thiocyanate maybe substituted. Likewise any other oxidizing agent or reagent known toliberate thiocyanogen from thiocyanates may be introduced as asubstitute for gaseous chlorine. Of the halogens, however, chlorine andbromine are preferred; fluorine is too hazardous and iodine is tooexpensive for practical use.

This method produced thiocyanogen, (SCN) in yields of 90-95 percent orbetter, based on the amount of thiocyanate salt reacted. There is littleor no hydrolysis. Losses due to polymerization of thiocyanogen are smallwhen reaction temperatures below about C. are used and are even smallerwhen temperatures of 10 C. or lower are maintained.

It is an important advantage of the invention that the thiocyanogen isobtained as a solution in an organic solvent, for such solutions can bestored and used later in the manufacture of insecticides andbactericides. For example, they can be used directly to produce1,2-dithiocyano-ethane, a wellknown bactericide, simply by introducingethylene and irradiating with a mercury vapor lamp.

EXAMPLE 2 The principles of the invention can also be embodied in batchprocesses. Thus, a mixture of grams of water containing 32.5 grams ofsodium thiocyanate and 195 grams of toluene was cooled to 5 C. Coolingwas continued while 15.9 grams of bromine were added slowly withstirring, the temperature being maintained at 510 C. When the reactionwas complete the mixture was allowed to stand until a solution ofthiocyanogen in toluene had separated as a layer above the aqueoussodium bromide solution. This layer was drawn off and there was obtained21.4 grams of thiocyanogen.

EXAMPLE 3 A glass lined reaction kettle equipped with a cooling jacketand an agitator was charged with a solution of l30 pounds of sodiumthiocyanate in pounds of water and 780 pounds of toluene were added. Thecharge was cooled to 5 C. and maintained at this temperature as 57pounds of chlorine gas was introduced with agitation.

At this point the mixture in the kettle was yellow and some solid sodiumchloride was present, indicating that the water was saturated with thissalt. Agitation was then stopped and the water phase separated and drawn05'.

Residual chlorine was then removed by flushing with nitrogen after which1 pound of diisopropyl peroxydicarbonate catalyst, dissolved in toluene,was added. Gaseous acetylene was then introduced, with continuedagitation, for about 45 minutes, during which time the temperature wasmaintained within the range of about 2 to 9 C. Another 1- pound portionof catalyst was then added and the introduction of acetylene wascontinued at the same temperatures for another 45 minutes. Agitation andacetylene introduction were continued while the batch was allowed towarm slowly to 25 C. The batch was then warmed slowly to 35 C. and heldat this temperature for 1 hour, after which it cooled to roomtemperature.

When the toluene was removed by vacuum evaporation there was obtained amoist-looking orange crystalline solid that melted at 7794 C. This wasidentified as vinylene bisthiocyanate. The wide melting point range andinfrared spectrum indicated a mixture of the cisand trans-isomers. Theyield was 73 percent, based on the weight of sodium thiocyanate charged.

Vinylene bisthiocyanate is known to be an effective algicide andbactericide; see US. Pat. No. 3,212,963.

Other alkynes may be substituted for acetylene without changing thenature of this process. Typical examples are methyl acetylene orpropyne, a gas, and heptyne (CH:C(CH CH and octyne (CH:C(CH CH which arecolorless liquids. Other monoalkyl acetylenes up to octadecyne(CH:C(CH), CH may be used. Arylacetylenes such as phenylacetylene anddiphenylacetylene may also be used.

It will be noted that in the first stage of this process thiocyanogen isproduced by the reaction in water solution of a halogen with a dissolvedwater-soluble thiocyanate salt such as an alkali metal, ammonium, oralkaline earth metal thiocyanate. For good results sufficient watershould therefore be present to dissolve the thiocyanate salt completely.It is also important, however, to form a concentrated solution of alkalimetal, ammonium or alkaline earth metal halide, as this assists therapid and complete extraction of thiocyanogen into the toluene or otherwaterirnmiscible organic solvent. For this reason it is greatlypreferable to add the thiocyanate salt as a concentrated aqueoussolution. In general, it is preferred to maintain a weight ratio ofalkali metal thiocyanate to water not greater than about 1.5 to 1 norless than about 0.3: l.

The ratio of water to toluene or other water-immiscible thiocyanogensolvent is also important. Three parts by weight of the solvent for eachpart of water is the preferred minimum amount that will producecommercially acceptable yields. Optimum proportions will depend on thetype of solvent; when benzene, toluene, ortho-xylene, meta-xylene orother liquid mononuclear aromatic hydrocarbons are used they are withinthe preferred range of three to 10 parts by weight of hydrocarbon foreach part of water.

EXAMPLE 4 A glass reaction flask equipped with a stirrer, a thermometerand a gas inlet tube was charged with a mixture of 25 grams of water,grams of toluene and 32.5 grams (0.4 mole) of sodium thiocyanate. Theflask was placed in an ice bath and maintained at 510 C. while 15.7grams (0.222 mole) of gaseous chlorine was introduced with agitation. Atthis point the reaction mixture was yellow and some solid sodiumchloride was present.

The flow of chlorine gas was then shut off and the system was flushedwith nitrogen. A solution of 0.52 grams of diisopropyl peroxydicarbonatecatalyst in 13 grams of toluene was added in two equal portions 45minutes apart as gaseous ethylene was passed into the mixture withagitation, the temperature being maintained between 2 and 9 C. After 90minutes the flow of ethylene was stopped, the ice bath was removed, andthe mixture allowed to stand for 3 hours. A total of 4.9 grams ofethylene had been added.

After separating the hydrocarbon solvent layer and removing the solventthere was obtained 23 grams of 1,2-dithiocyanoethane, a bactericideknown to be effective against such bacteria as Aeorbacter aerogenes andPseudomonas aeruginosa.

A wide variety of monolefin hydrocarbons may be substituted for theethylene in this process. Thus any alphaolefin of from three to 18carbon atoms and having the formula where R is an alkyl radical and R ishydrogen or alkyl may be used, such as propylene, l-butene, isobutylene,l-amylene, pentylethylene, octylethylene, and the like. lntemal olefins,aryl-substituted olefins such as styrene, and cyclic unsaturatedhydrocarbons such as cyclopentene, cyclohexene, cyclooctene and terpenessuch as beta-pinene may also be used.

What I claim is:

1. A method of producing thiocyanogen which comprises generatingthiocyanogen in an aqueous solution of a watersoluble thiocyanate salthaving a water-insoluble liquid organic thiocyanogen solvent admixedtherewith, thereby extracting the thiocyanogen from the water phase intothe organic solvent phase as it is formed, and separating the resultingorganic solvent solution from the water phase.

2. A method of producing thiocyanogen by reacting a halogen with awater-soluble thiocyanate salt dissolved in water having awater-insoluble liquid organ thiocyanogen solvent admixed therewith,thereby extracting the thiocyanogen from the water phase into theorganic solvent phase as it is formed, and separating the resultingorganic solvent solution from the water phase.

3. A method of producing thiocyanogen which comprises generatingthiocyanogen by reacting a halogen with a watersoluble thiocyanate saltselected from the group consisting of ammonium thiocyanate, alkali metalthiocyanates and alkaline earth metal thiocyanates, said salt beingdissolved in water having a liquid mononuclear aromatic hydrocarbonadmixed therewith, thereby extracting the thiocyanogen from the waterphase into the hydrocarbon phase as it is formed, and separating fromthe water phase the resulting solution of thiocyanogen in thehydrocarbon.

4. A method according to claim 3 wherein the weight ratio of thethiocyanate salt to the water is such that a substantially saturatedaqueous salt solution is produced.

5. A method according to claim 3 in which the weight ratio of thehydrocarbon solvent to the water is between 3 to l and 10 to l.

6. A method according to claim 3 in which the halogen is chlorine.

7. A method according to claim 3 in which the aromatic hydrocarbon istoluene.

8. A method according to claim 3 in which the thiocyanate salt is sodiumthiocyanate.

9. A method according to claim 3 in which the water is maintained at atempera tur: beJQv ZOZC.

2. A method of producing thiocyanogen by reacting a halogen with awater-soluble thiocyanate salt dissolved in water having awater-insoluble liquid organ thiocyanogen solvent admixed therewith,thereby extracting the thiocyanogen from the water phase into theorganic solvent phase as it Is formed, and separating the resultingorganic solvent solution from the water phase.
 3. A method of producingthiocyanogen which comprises generating thiocyanogen by reacting ahalogen with a water-soluble thiocyanate salt selected from the groupconsisting of ammonium thiocyanate, alkali metal thiocyanates andalkaline earth metal thiocyanates, said salt being dissolved in waterhaving a liquid mononuclear aromatic hydrocarbon admixed therewith,thereby extracting the thiocyanogen from the water phase into thehydrocarbon phase as it is formed, and separating from the water phasethe resulting solution of thiocyanogen in the hydrocarbon.
 4. A methodaccording to claim 3 wherein the weight ratio of the thiocyanate salt tothe water is such that a substantially saturated aqueous salt solutionis produced.
 5. A method according to claim 3 in which the weight ratioof the hydrocarbon solvent to the water is between 3 to 1 and 10 to
 6. Amethod according to claim 3 in which the halogen is chlorine.
 7. Amethod according to claim 3 in which the aromatic hydrocarbon istoluene.
 8. A method according to claim 3 in which the thiocyanate saltis sodium thiocyanate.
 9. A method according to claim 3 in which thewater is maintained at a temperature below 20* C.